With the evolving and developing of the conventional Dense Wavelength Division Multiplexing (DWDM) optical transmission system, the transmission with higher speed (≧40 Gbit/s) implemented in a single channel has become a clearer direction for the evolution thereof. In the evolution direction, an important technology is the high speed optical signal processing at the receiving end of the channel, i.e. how to transform efficiently the high speed optical signal into the information which is recognizable by the receiving chip. Wherein, the following technologies may be involved:
1. since the dispersion tolerance of the high speed transmission system is exponentially reduced, more accurate channel dispersion compensation technology is needed, i.e. accurate dispersion complementation technology.
2. since the front end of the receiver needs to be adjusted to a suitable power level as needed by the receiving module, the power control technology is needed.
3. since the receiving level of the receiver needs to be adjusted according to the received signal to ensure the error correction error ratio to be roughly identical, the receiving level control technology needs to be used.
4. a demodulation technology related closely to code type needs to be used, for example, for the DPSK code type, there is the Delay Interferometer (DLI) control technology.
5. a phase modulation technology for the received signals needs to be used to achieve optimal Clock and Data Recovery (CDR) effect by adjusting the phase of receiver.
In conclusion, many conditions may influence the final data receiving result at the receiving end processing the high speed optical signals, and the restraining and balancing factors between various conditions are very complicated, thus an accurate result may be difficult to obtain by the way of simulation. Presently, in practical applications, the trial and error procedure is mainly used, that is, the receiving characteristics are observed in various conditions by configuring different parameters for various factors, until the suitable receiving balancing point is found.
However, the method has the following disadvantages: the combination trial and error algorithm is so complicated that it takes a long time to reach the optimal receiving area of the system, and sometimes the process of parameter adjustment will cause the case that the receiving characteristics differ greatly and the performances are frequently repeated. When the receiver is changed by another with different type, the whole system must search for a new optimal receiving balancing point again.